1. Field of the Invention
The invention relates to an expandable anchoring device to be inserted in and fastened within a bored hole, said device comprising a tubular anchoring member moulded from a deformable plastics material and being provided with an internal abutment or shoulder and a thread portion for cooperating with a screw, longitudinally extending slits or slots being provided in the wall of said anchoring member.
2. Description of the Prior Art
Such an anchoring device is disclosed in for example U.S. Pat. No. 2,918,841. Anchoring devices of said type are used in cases where an object is to be fastened to thin walls, plates or panels, the back of which is inaccessible or accessible only with difficulty for example, wall elements formed by spaced panels or plates defining between them a cavity which may be filled with a soft or crisp insulating material. The slits or slots of the anchoring member may for example, be axially or helically extending, separate the wall of the anchoring member into strip-formed or band-formed parts. When an anchoring device of the type described is inserted in a bored hole in a wall or plate in such a manner that the inserted end portion of the anchoring device projects beyond the back of the plate or wall and the deformable anchoring device is then compressed by screwing the screw into engagement with the thread portion of the anchoring member, the inner end of the anchoring member will be moved in relation to the plate or wall, and the anchoring member will mainly tend to bulge at that inner end being moved, whereby the strip-formed or band-formed parts at the projecting end portion of the anchoring member are bended outwardly and form against the back of the plate an abutment, and thereby an object of some kind may be fastened to the accessible front of the plate or wall.
When a fastening device of the type described is mounted in a plate of a relatively soft material, such as a plasterboard and the screw is vigorously tightened the expanded parts of the anchoring device forming the said abutment against the back of the plate will be pressed into the back of the soft plate whereby the plate may be damaged. If, alternatively, the anchoring device is mounted in a plate of a relatively hard material, such as a plate or hardened masonite or a plywood panel, a vigorous tightening of the screw may cause cutting of the bended band-formed parts of the anchoring member because said parts are pressed against the edges around the bored hole. If the band-formed parts are cut, the anchoring device will of course become ineffective.
Furthermore, various types of dowels or wall plugs adapted to be mounted within non-through holes in solid walls are known. The effect of these dowels or wall plugs is based on the fact that their inner diameter is smaller than the outer diameter of the core of the belonging screw -- which is normally a self-tapping screw such as wood screw -- and thus the dowel is expanded radially when the screw is screwed into the same whereby the dowel is wedged in the bored hole. The pressure thereby exerted on the wall material may cause peeling of wall material around the mouth or entrance of the bored hole, unless the outer end of the dowel is pushed inwardly so as to be spaced from the said entrance of the hole. Furthermore, when using the said dowels, it is not possible to obtain a satisfactory wedging within a bored hole if the inner diameter of the same substantially exceeds the outer diameter of the dowel.